JPS6136067B2 - - Google Patents

Description

[Detailed description of the invention]

This invention features Fe with high density and high magnetic properties.
-Regarding a method for producing a Cr-Co based sintered magnet alloy. Fe-Cr-Co-based sintered magnet alloy has been developed as a material that has excellent magnetic properties comparable to Alnico 5 magnet alloy and can be processed in hot and cold processes, and is already used in many directions today. ing. Possible methods for industrially manufacturing this type of magnetic material include rolling, casting, and sintering. First, the rolling method is a method that is not possible with alnico-based or ferrite-based magnetic alloys, but as a method that takes advantage of the unique properties of the Fe-Cr-Co system, we propose various improvement methods and the necessary additive components. has been done. However, since the rolling method involves complicated processes such as forging, rolling, and annealing, it is not suitable for mass production and tends to be expensive, so it is generally applied to special shapes such as plate shapes and wire shapes. Furthermore, various additive components are required to prevent oxidation and nitridation of Cr during melting and heat treatment during the manufacturing process. The following technology is known as this rolling method. Special Publication No. 53-35536, No. 50-101217, No. 54-20934, No. 51-38221. Next, the casting method is generally applied to hard and brittle materials such as alnico-based materials. Fe
-Cr-Co is ductile and has high toughness, so when casting method is used, it becomes difficult to remove the casting from the runner, and there are also problems such as sand build-up and around the molten metal. Casting defects have also become an unavoidable problem. In addition, it is not satisfactory in terms of workability and efficiency, and it is also problematic in terms of economy, as various additive components must be used to prevent Cr from forming and nitriding during melting. There is. For example, even in the case of JP-A-52-49925, which exhibits excellent magnetic properties by selecting specific additive components, the above-mentioned problems still exist. On the other hand, the sintering method does not have the above-mentioned problems found in the rolling method and the casting method, and is industrially applicable to large amounts of Fe-Cr.
- Suitable for producing Co-based magnets. However, it is known that there are problems with sintered density and magnetic properties. Therefore, for example, Japanese Patent Application Laid-open No. 1983-
33205, as seen in JP-A-53-43006, B,
It has been proposed to add Si, C, etc., but in these cases the density can be improved, but the magnetic properties only obtain a value of (BH)m5.0MGO or less. In addition, in conventional sintering methods, the Co content was generally more than 20%, making it expensive. The purpose of this invention is to propose a method for manufacturing an inexpensive Fe-Cr-Co sintered magnet alloy suitable for industrial mass production, and furthermore, even with a sintered magnet, the theoretical density ratio is 97. % or more and (BH) m5.0MGO
The purpose of this study is to propose a method for producing a Fe-Cr-Co sintered magnetic alloy having the above magnetic properties. Thus, the present invention provides a method for producing a Fe-Cr-Co based sintered magnet alloy by a powder metallurgy method, which is composed of 20 to 35% Cr, 3 to 15% Co, the balance Fe and unavoidable impurities, and has a mesh weight of 200 mesh or less. After mixing the main raw material powder with the particle size of
It is characterized by performing sintering at 1450°C, and immediately after cooling between 800°C and 500°C at a cooling rate of 5°C/min or more, magnetic field isothermal treatment and aging treatment are performed.
This is a method for manufacturing a Fe-Cr-Co based sintered magnet alloy. 20% to 35% Cr in the alloy composition is 20% to 35%.
This is because if it exceeds 35%, the residual magnetic flux density and coercive force required for the magnetic alloy cannot be obtained. In addition, the reason for setting Co3 to 15% is that if the Co content is less than 3%, the residual magnetic flux density and coercive force required for a magnet alloy cannot be obtained, and if it exceeds 15%, high density This is because it is impossible to achieve this goal, and furthermore, the price is too high to be practical.
The remainder is Fe, and the method of this invention does not require substantially any other additional components. The reason why no additional components are required in this invention is considered to be due to the combined effect of the following points. (1) Because it is sintered in a vacuum or in a non-oxidizing atmosphere, it is hardly affected by the external atmosphere: Fe-Cr-Co alloys contain Cr, so they are susceptible to oxidation and nitriding; Since melting and heat treatment steps are essential in conventional rolling and casting methods, additive components are essential to prevent the adverse effects of oxidation and nitriding. However, in the sintering method of the present invention, no melting or solution treatment is performed, so it is hardly affected by oxidation or nitriding. The sintering atmosphere preferably has a total oxygen or nitrogen concentration of 3 ppm or less; this is true if it is in a vacuum.
The degree of vacuum is 10 ^-3 mmHg or less, which corresponds to a dew point of -70°C or less in H ₂ or inert gas, and is an atmosphere that can be easily obtained both industrially and experimentally. (2) As raw material powder, fine raw material powder mainly consisting of particle size of 200 mesh or less, i.e. Fe-Cr powder or
Use of Fe-Cr-Co powder: When using raw material powder with a particle size of about 100 mesh, which has been conventionally used, it is possible to create a high-density powder without any additives.
Although it has been difficult to obtain a Fe-Cr-Co sintered magnet alloy, high density can be easily obtained by using raw material powder with a particle size of 200 mesh or less. In general, making the raw material powder finer increases the cost of powdering, which is undesirable, but it is not so difficult to obtain Fe-Cr or Fe-Cr-Co powder of 200 mesh or less. Especially in Fe-Cr series or Fe-Cr-Co series alloys, 40
Brittle σ that forms over a wide range of Cr content of ~60%
Alloys mainly consisting of (sigma) phase can be easily pulverized, and it is also easy to obtain powder with a particle size of 200 mesh or less. (3) There is no need to perform solution treatment, so there is no adverse effect of the atmosphere during heat treatment: This is because sintering is performed in a vacuum or in a non-oxidizing atmosphere, and the adverse effects of oxidation and nitridation are avoided. This has the effect of eliminating the need for additional elements to prevent this and facilitate heat treatment. By the way, according to the present invention, the solution treatment of the sintered body can be omitted, but in order to do so, when heat treating the sintered body, the temperature range between 800 and 500°C after sintering is heated at an average rate of 5°C/min or more. Must be cooled.
If cooling is performed at a slow cooling rate of less than 5° C./min, the magnetic properties will deteriorate and the object of the invention will not be achieved. Generally, by air cooling, 5
A cooling rate of ℃/min or higher can be obtained. In this invention, it is preferable to use a surface-active powder as the raw material powder. for example,
The water atomization method is a powerful industrial mass production method for producing raw material powder, and has been proposed in the past (Special Publication No. 12300/1983), but the powder produced by the water atomization method has a surface that is Because it is oxidized, C and B are required to improve the sintered density.
The magnetic properties obtained were of a low level. However, according to the present invention, as long as the particle size is 200 mesh or less even for powder made by water atomization, high density and high magnetic properties can be obtained by making the powder active on the surface through heat treatment etc. I can do it. Further, by using carbonyl iron powder as the raw material iron powder, it becomes easy to obtain high density without using any additional components. In addition to carbonyl iron powder, atomized iron powder, electrolytic iron powder, reduced iron powder, etc. can be used as the raw material iron powder. In general, carbonyl iron powder has a fine particle size and high activity, so it is expected that high density can be obtained, but it is possible to obtain high density by blending it with about 100 mesh Fe-Cr powder or Fe-Cr-Co powder. In this case, a satisfactory degree of high density cannot be obtained.
In this invention, the sintering temperature is preferably 1250 to 1450°C in order to obtain high density and high magnetic properties. i.e.
This is because the sintered density is low below 1250°C, and deformation occurs when the temperature exceeds 1450°C. As described above, according to the present invention, a high-density Fe-Cr-Co-based sintered magnet alloy was obtained without the need for additive components.
When we examine the effects of adding Ti, Si, Mn, Cu, Sn, etc., which have been proposed to be effective when added to magnet alloys, it is clear that none of them have any effect on improving properties. Summer. This is a point in which the magnetic alloy obtained by the present invention is essentially different from conventionally proposed Fe--Cr--Co based magnetic alloys which required various additive components. Examples according to the present invention will be shown below to clarify its effects. Example 1 Sigma powder consisting of 48% Cr, 18% Co, and the balance Fe was mechanically crushed to a size of 200 mesh or less, and this was mixed with carbonyl iron powder with an average particle size of 5 μ or less and Co powder of 400 mesh or less to obtain 25% Cr, A mixed powder adjusted to a composition of 9.5% Co and the balance Fe was 5000Kg/cm ²
It was pressure molded into a shape of 13 mm (diameter) x 10 mm (length) at a pressure of Next, this is placed in a vacuum of 10 ^-3 Torr.
Sintered at 1350℃ for 2 hours, then heated to 800-500℃ after sintering.
was cooled by changing the cooling rate. The obtained sintered body was then heated at 640℃ without solution treatment.
After 1 hour of magnetic field isothermal treatment at 3000Oe, further 620Oe
It was cooled and maintained at a rate of 3°C/hr from 500°C to 500°C. The results of examining the characteristics of the magnet thus obtained are shown in Table 1 below.

[Table] Example 2 Add 350 to the mixed powder prepared in the same manner as Example 1.
TiH ₂ (Ti96%) powder with less than 250 meshes, Fe-Si alloy with less than 250 meshes (Si76.7%, remaining Fe), Fe-Mn alloy with less than 250 meshes (77.3% Mn, remaining Fe)
Powder, also less than 250 mesh electrolytic copper powder, 200
0.5 for each Sn powder of mesh size or less,
A mixed powder with an adjusted composition of 25% Cr, 9.5% Co, and the rest of the added elements and Fe was press-molded in the same manner as in Example 1, adding 1.0 and 2.0 wt%. Next, this is heated to 1300℃ or 1350℃ in a vacuum of 10 ^-3 Torr.
After sintering, the material was sintered for 4 hours, and after sintering, it was cooled at a cooling rate of 20°C/min between 800 and 500°C. Among the obtained sintered bodies, those sintered at 1300℃ were not subjected to solution treatment, and those sintered at 1350℃ were
Solution treatment at 1250℃ for 20 minutes, followed by 640℃
C. or 645.degree. C. and 3000 Oe for 1 hour in a magnetic field, and then held at 620.degree. C. for 1 hour, and then cooled from 620.degree. C. to 500.degree. C. at a rate of 3.degree. C./Hr. The results of examining the characteristics of the magnet thus obtained are shown in graphs in the accompanying drawings. The graph in the attached drawing shows the relationship between the additive elements and their amounts and the magnetic properties by comparing them with the above-mentioned sintering temperature and magnetic field isothermal treatment temperature.
and △ (open triangles) indicate the case where the sintering temperature was 1300°C without solution treatment, and ● (black circle) and ▲ (black triangle) indicate the case where the solution treatment was performed at the sintering temperature of 1350°C. Furthermore, the differences in magnetic field isothermal treatment temperature are as follows: 〇 (white circles) and ● (black circles) indicate the case of 640°C, and △ (open triangle) and ▲ (closed triangle) indicate the case of treatment at 645°C. As is clear from the graph shown in the drawing, Ti, Si,
In the case of any of the additive elements Mn, Cu, and Sn, the magnetic properties decrease as the amount added increases, and the best magnetic properties are obtained when no additive is added at all. The present invention has been described in detail above. According to the present invention, for example, as can be seen from the results shown in Table 1, when cooling a sintered body, the cooling rate is 5°C/5°C between 800°C and 500°C. If it is more than min, good magnetic properties, especially maximum energy product, can be obtained, and therefore, the solution treatment after sintering, which has been conventionally required, can be omitted. Furthermore, as can be seen from the results shown in the addition drawings, in this invention, which does not involve solution treatment, by adding various additive elements, the theoretical density ratio and magnetic properties, especially the magnetic energy product, coercive force, and Both magnetic flux densities decrease.

[Brief explanation of the drawing]

The attached drawing is a diagram showing the relationship between the amounts of Ti, Si, Mn, Cu, and Sn added and the magnetic properties.

Claims (1)

[Claims] 1 In a method of manufacturing Fe-Cr-Co based magnet alloy by powder metallurgy, Cr20-35%, Co3
~15%, balance consisting of Fe and unavoidable impurities
After mixing raw material powder mainly having a particle size of 200 mesh or less and press forming, sintering is performed at 1250℃ to 1450℃ in a vacuum or non-oxidizing atmosphere. 1. A method for producing a Fe-Cr-Co based sintered magnet alloy, which comprises performing an isothermal treatment in a magnetic field and an aging treatment immediately after cooling at a cooling rate of 5° C./min or more.